In recent years, with the multimediatization of information in cellular mobile communication systems as represented by mobile phones for example, transmitting high capacity data such as still images and movies in addition to speech data has become a norm. To realize high capacity data transmission, a technology of realizing a high-transmission rate using a high-frequency radio band is studied actively.
However, when a high-frequency radio band is used, although a high transmission rate can be expected in a short distance, attenuation due to transmission distance becomes greater as the distance increases. Accordingly, when a mobile communication system utilizing a high-frequency radio band is actually operated, the coverage area of each base station becomes smaller, which then requires setting up a larger number of base stations. Since the setup of base stations involves large costs, a technology is strongly demanded for realizing communication services which control an increase in the number of base stations and utilize a high-frequency radio band.
To meet this demand, studies are underway for relay technologies of providing relay stations between a mobile station and a base station, and allowing communication between the mobile station and the base station via these relay stations. Moreover, one of these relay technologies is cooperative relay where a plurality of relay stations relay in cooperation between the relay stations. In cooperative relay, a receiving apparatus receives relay signals from a plurality of relay stations, so that diversity effect can be obtained even when each relay station has a single antenna. Moreover, studies are underway for a technique adopting space time encoding using STBC (Space Time Block Code) for cooperative relay for improving diversity effect, assuming a plurality of relay stations performing cooperative relay a plurality of antennas (see Non-patent Document 1). Cooperative relay may be also referred to as “collaborative relay.” Non-patent Document 1: Tsuyoshi MIYANO, Hidekazu MURATA, and Kiyomichi ARAKI, “Cooperative Relaying Technique with Space Time Block Code for Multihop Communications among Single Antenna Terminals,” TECHNICAL REPORT OF IEICE, A•P2003-342, RCS2003-365, pp. 71-76, 2004-03)